Abstract

A failed wheel nut belonging to an aircraft was sent to the laboratory for investigation. Examination revealed that the wheel nut failed in progressive manner wherein a number of cracks had initiated all along the circumference of the nut at the fillet of the flange. Fractographic features indicated that the reason for the progressive failure was hydrogen embrittlement and it appears most probable that the wheel nut would have picked up hydrogen during cadmium plating. In general, the microstructure of the nut material was found to be satisfactory and the composition was found to conform to the specification. A detailed analysis of the failure is presented in this report